In many cases, the writer is also a producer, and composes - and often records - the entire track on their own. Then, the vocals are added by whichever singer takes the song. Basically, there's not a 'band' in the first place.

Bermuda

THIS.... SOOOOO MUCH OF THIS!

I can't tell you how many artists I've played for over the years that either "A" don't know who even put together and played on their tracks, or "B" had a Producer write and record all their songs, then just had the singer come in and lay down the vocals.

Then when it comes time to perform live they hire musicians so it does't look like they are just singing karaoke.

I did a session for an artist at the beginning of September that was exactly that. I was just lucky enough that the artist wanted me to record live drums in place of the programed ones her producer typically does.

The thing is, it's always been a person against the computer. There's partial human interaction required. Has anyone made a program where the computer plays chess with itself? Would there be a point?

Mostly it's been different computers playing games against each other. For a long time now there is an (I believe) annual computer chess championship where the winning software is awarded a prize.

However! An interesting new thing recently occurred. The concept of "deep learning" was applied to a chess program. Rather than program it with all sorts of rules and heuristics, the developer had it play itself over and over and learn how to get better. After three days, it reached International Master level (which is really high). It's not the best chess computer out there, but it would beat the crap out of all but a tiny number of people.

Reason #1: It's insanely cheap. You pretty much pay one guy to come in and make a beat for you, and it's usually the same guy who has a hand in producing it. You can afford to get a studio that's basically just a small room and a vocal booth, instead of having to accommodate a piano, 10-12 guitars, maybe 2-3 kits and a dozen or so snare drums.

Reason #2: It's more accurate than a real drummer. Even the best studio guys out there have slightly imperfect time, but the machine does not. It's also easier to send the music off and know with 100% certainty that the parts are completely in time.

Reason #3: You can get way more complicated with the parts. I know the guys in Steely Dan were complaining about having to work with so many different drummers to get what they wanted out of the song, and they asked a producer if there was just some machine they could program to get it right.

As mentioned above, this is a trend in pop music, as it was in the 80's. It will likely pass and you will perhaps see more albums recorded with real drums again. Bruno Mars actually does use real drums in a lot of his songs, and in some cases (such as Uptown Funk) he just plays them himself. Guys like Questlove and Jojo Mayer are already pushing against computer generated beats by playing insanely complex grooves, but they're also grooves with a lot of feel that can't be replicated, thus giving them work.